Current medical practice commonly employs the procedure for surgical correction of diseases of the heart, lungs and liver. Many of these surgical procedures involve massive interruption or disruption of the blood flow of the patient. These procedures frequently require support of the normal cardiovascular function of a patient. Such involvement might be necessary where the surgical procedure involves repair of various heart and vascular organs. During open heart surgery, as an example, a surgeon needs a procedure for insuring a constant flow of blood to the patient while the surgery is being performed on the heart, including the valves and blood vessels of the heart. In such surgery, blood flow support is a common procedure used to insure that adequate blood flow is sustained in the patient's body in order to maintain vital organ functions.
Organ transplant surgery also has become a common medical practice which requires the interruption or disruption of the normal blood flow in a patient. Success of organ transplant of kidneys, liver and the heart requires successful sustaining of the normal blood flow of a patient. This blood flow interruption is sufficiently critical that common surgical procedures require that blood flow assistance to the patient be utilized during the procedure.
The ancillary blood flow assistance to the patient normally involves a blood flow pump used to replace or assist the function of the heart during the course of the procedure. Such blood flow assist requires that the blood flow be monitored at all times during the procedure to insure that the proper flow of blood is occurring in the cardiovascular system to prevent unnecessary complications for the patient and to insure adequate blood flow to vital organs during the course of surgical procedure.
One of the vital conditions which must be observed throughout the course of supplementary assistance to the cardiovascular function of a patient is a monitoring of the blood flow in the patient's body as the patient's system is being assisted by an artificial blood pump. A part of this entire system involves a blood flow monitoring system capable of sensitive and continuous monitoring of the blood flow from the pump assist even as the flow rates of the assistance to the patient are at relatively low levels.
The use of electromagnetic flow meters to measure blood flow is known in the medical arts and the basic concept of such measurement was described in U.S. Pat. No. 2,149,847. Because of the composition of blood, it is well known that passing a volume of blood, either in a tube or in a blood vessel at right angles to an established magnetic field will result in the production of an electromotive force (EMF) or induced voltage which is produced in a direction mutually perpendicular to the magnetic field and the direction of the blood flow. As indicated, the blood has the characteristics of a moving conductor and acts the same as passing an electrical wire conductor through a magnetic field. Voltage is generated in a fixed cross-sectional area which is proportional to the average velocity of flow of the blood resulting in a measure of the volume rate of flow of the blood through the tube or blood vessel. This voltage can be sensed by electrodes positioned at diametrically opposite points along the tube or lumen, when the electrode tips in contact with the flowing blood are positioned perpendicular to the direction of the magnetic field.
An important feature of the prior art involves the positioning of the electrodes, magnetic structure, and the blood flow at a fixed pre-determined relationship in order to maintain an accurate calibration of the blood flow. Past practice has dictated that the assembled tubes, electrodes and magnetic structure be constructed as a unitary assembly which insures the proper measurement of blood flow. This unitary structure incorporates several serious disadvantages in the practice of medicine since it presents problems of sterilization of the blood flow measuring device itself as well as creating limitations to blood flow-rate sensitivity capabilities.
Ideally, a flow monitoring system should include a method whereby the sensing unit immediately in contact with the patient's blood should be disposable so that each patient can be provided with a flow detection unit which is completely sterile and is not merely a unit which has been subsequently cleaned after previous surgical procedures. Cleaning such units presents serious contamination problems since the success of an operation may be based upon the quality of the sterilization and cleanliness of apparatus used during the surgical procedure. Therefore, it is common in surgical procedures to use newly manufactured and sterilized units which are then discarded after each surgical procedure. This insures maximum sterilization of the implements used during the course of the procedure and eliminates, as much as possible, the likelihood of transmission of communicable diseases and other infections from patient to patient. Use of a disposable flow device greatly enhances the likelihood of success of the surgical procedure.
The devices which monitor blood flow frequently involve electrical terminals, conduits, similar materials, and geometrics which are extremely difficult to sterilize and which, if they are sterilized, are totally dependent on the skill and care of a number of participants in the sterilization process. Not only does the sterilization depend upon the initial cleaning process but it also depends upon the type of sterilization practice employed to clean the device. Further, following initial sterilization, the successful use of such reusable devices depends upon the care with which the unit is stored. Consequently, disposable units which are discarded after each surgical procedure are likely to greatly enhance the success of a surgical procedure.